open source disk crypto update

[Alexander Klimov]

On Thu, 26 Apr 2007, Simon Josefsson wrote:
> > Are you afraid of attackers secretly changing your software (to
> > monitor you?) while your computer is off?
>
> I believe this is a not completely unreasonable threat.  Modifying files
> on the /boot partition to install a keylogger is not rocket science, and
> (more importantly) can be done remotely, if you gain unauthorized access
> to the machine.

It is almost impossible to modify computer remotely once it is off. It
is possible to destruct computer physically (or by EM pulse), it is
possible to interact with computer remotely if `off' is actually some
kind of stand-by with lamps off. But once you disconnect your computer
from the power supply it should be immune from remote attackers. ``The
truly secure system is one that is powered of, ... and even then I
have my doubts.'' :-)

In most cases once computer can be compromised remotely, it is
already booted, and since disk encryption is transparent once the
computer is booted, it cannot change how easy it is to install
a root-kit remotely.

> If you boot from a trusted USB stick instead, and check the
> integrity of the hard disk, the attacker needs to modify BIOS in
> order to install the keylogger.  This may be sufficient difficult to
> do on a large scale (there are many different ways to update BIOS
> software), so that the attacker goes away to try some other weakness
> instead.

In this case you ensure integrity using a tamper resistant hardware
(assuming you always carry your USB stick with you). By the way, a
non-rewritable CD should be even better.

-- 
Regards,
ASK

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